It's been called a "lightbox," a man-made ancient aperture in a tomb
that accurately tracks the movement of celestial bodies on the darkened
chambers inside.

The BBC reported Wednesday that the third of such phenomena has been
discovered in Ireland by a researcher and artist from County Sligo.

Earlier this year, the network reported on the discovery of a similar "lightbox"
in Scotland by archaeologists from Glasgow University. That prehistoric,
manmade formation captured the rays of the Sun at the start and end of
the winter.

But the new discovery in Ireland, found by Martin Byrne at Carrowkeel,
is even more elaborate than the other two known lightbox tombs. Not only
does it capture the Sun's beams for three months in summer, the aperture
is designed to capture the beams of the setting, full Moon at the winter
solstice. The most complex of those discovered, the Irish "lightbox"
reveals "astonishingly-detailed astronomical knowledge of the ancient
people," said the BBC.

The tomb is believed to originate in the Neolithic era 6,000 years ago,
set into a cairn in one of the most scared regions of ancient Ireland.
Capturing moonbeams inside the chamber of the tomb apparently was no
accident on the ancients' part, Byrne believes. The cairn faces a hill
known as

Knocknarea, which means "Hill of the Moon." Other nearby landmarks also
take their names from lunar roots.

And the new discovery indicates that not only were the ancients accurate
in their fashioning of the lightbox, they were also patient. "Building
it would have required many years of observations of the motions of the
Moon by the tomb's architects," says Byrne. The tomb points to the most
northerly point the setting Moon reaches on the horizon, an event that
only happens every 18.6 years.